Magnetic media hard disks have in recent years become a standard peripheral to computer systems, large and small. A typical current generation hard disk consists of one or more semi-rigid platters that are coated with particles capable of being magnetized to encode information. Each of the platters typically has a hole permitting the multiple platters to be placed onto a spindle, so that they are stacked in substantially parallel planes. Each platter may have up to two surfaces that can be magnetized, so that a typical hard disk consisting of n platters is capable of having 2n surfaces available for the reading and writing of data. The data magnetically encoded onto the platters is typically read or written by a single head, or series of heads, such as Magneto Resistance (MR) effect heads, well known in the art.
Each hard disk surface is physically divided into a series of concentric tracks running from the inner diameter to the outer diameter. The number of tracks may depend on the disk manufacturer. Moreover, rapidly changing technology in this area has permitted an increase in disk density (e.g. tracks per inch or bits per inch). A hard disk is also logically divided into a series of fields which are accessible by the head, and which are largely defined by the process of formatting. A typical hard disk will have both servo fields and data sector fields. Servo fields permit the head to locate itself onto the center of the track before attempting to access the data sectors. Data sectors are typically established by the formatting process, with each sector containing 512 bytes of information in a DOS-based computer system.
There are numerous approaches to the configuration of the various fields in a hard disk. Each of these approaches involves tradeoffs in simplicity, data density efficiency and disk seek time. The logical configuration of the data sectors may be pursuant to what is known in the art as header-type formatting or headerless formatting. Header-type formatting provides for each data sector to include an identification header that uniquely identifies that data sector, thus permitting the drive logic to determine when the magnetic head has reached a particular sector. The data sectors can be allocated onto the disk tracks pursuant to constant frequency recording (CFR) or constant density recording (CDR). The CDR approach is further refined in Zone Density Recording (ZDR), wherein the platter is logically divided into a series of zones of concentric tracks. Each zone has a different recording frequency and data separation, but each track within a zone has the same number of sectors. Strange, et. al., U.S. Pat. No. 5,627,946, "Hard disk format using frames of sectors to optimize location of servo bursts," and Harris, U.S. Pat. No. 5,422,763, "Split field zone data recording," both contain helpful discussions pertaining to the various formatting schemes for hard disks, and are hereby incorporated by reference.
Because header-type formatting provides that each data sector must be appended with its own identification information, the overall data efficiency of the disk is significantly reduced. As a result, current HDD's are most often formatted for a headerless configuration. In a headerless HDD system, each data sector does not have a header identification segment. However, the platter still has a number of servo fields that are now further used to calibrate timing logic in the disk controller to locate specific data sectors.
FIG. 1 refers to one possible configuration for a headerless disk system. The hard disk has a number of platters 100, and a series of heads 120 corresponding to each readable/writable surface. The surface of platter 140 is divided into one or more zones 245, 250 and 255, in this example three zones, each zone containing a number of tracks. The surface is also divided into a number of servo wedges 160, each of which defines servo fields in each track radiating from the inner to the outer diameter. In this example there are six servo wedges. Between each pair of servo wedges 160, there is a data wedge 180, which defines one or more data sectors in each track radiating from the inner to the outer diameter of the surface. On each track 220 within the data wedge there is one or more data sectors 200. As can be appreciated from the figure and the previous discussion, the physical and logical layout of the magnetic media is subject to wide variation and constant change. Magnetic media may differ according the number and configuration of servo/data wedges, tracks (e.g., tracks per inch or tpi), sectors per track (e.g., bits per inch or bpi), etc. For example, the wedge based logical layout may be substituted with a different tracking/geometry scheme.
As the previous discussion demonstrates, the magnetic disks in the HDD can be configured in numerous different fashions. The HDD system must be compatible with the particular disk formatting scheme employed. In particular, the disk controller will include a disk formatter that must be configured (hardware and software) in conformance with the format of the magnetic media. This creates a great challenge to the designer of disk controllers, and disk formatters, in particular, which must be compatible with the magnetic media with which they are integrated. Moreover, even when disk manufacturers have maintained the same basic formatting scheme, advances in technology such as increases in tpi or bpi will require changes to the disk controller, especially the disk formatter, that interfaces between the magnetic media and the general host computer. As a result, the architecture of prior art disk controllers has been such that substantial modifications to hardware and/or substantial, and complex, reprogramming of firmware has been required each time a disk controller is integrated with a physically different magnetic media (e.g., more platters or more data density, etc.) or logically different magnetic media (e.g., changes in disk layout or format). In addition to these general data formatting differences, each vendor may have unique formatting schemes for diagnostic tasks.
What is desired, therefore, is an efficient, highly programmable disk formatter that efficiently allocates processing resources between processors, while remaining flexible and user friendly, and that is programmable using a pre-defined instruction set, specially adapted for the disk formatter application, that can accommodate changes from disk to disk or format to format. One benefit of such a disk formatter is that the disk drive manufacturer need not be required to repeatedly redesign the disk formatter to accommodate different or next generation drive programs.